Humidity resistant photoconductive compositions

ABSTRACT

IMPROVEMENT IN THE HUMIDITY RESISTANCE OF PHOTOCONDUCTIVE TITANIUM DIOXIDE CONTAINING ELECTROGRAPHIC ELEMETS IS ACHIEVED BY COMBINING THEREWITH A CARBOXYLIC ACID OR METAL SALT THEREOF SUCH AS ABIETIC ACID OR ZINC ABIETATE WITH AN INORGANIC METAL OXIDE SUCH AS ZINC OXIDE.

y 1973 o. w. GOSSELINK ETAL 3,736,134

IiUMlDITY RESISTANT PHOTOCONDUCTIVE COMPOSITIONS Filed Oct. 14, 1970 1' N YEA/TOPS DON/4L0 W GOSSEL/NK FINA/R B HORNE KJMM A T TOR/V5 Y5 United States Patent Int. Cl. G03g 5/08 US. Cl. 961.8 17 Claims ABSTRACT OF THE DISCLOSURE Improvement in the humidity resistance of photoconductive titanium dioxide containing electrographic elements is achieved by combining therewith a carboxylic acid or metal salt thereof such as abietic acid or zinc abietate with an inorganic metal oxide such as zinc oxide.

This invention relates to photoconductive compositions and more particularly, to photoconductive compositions having improved humidity resistance.

Photoconductive compositions are utilized in numerous electrographic processes both as intermediate and final receptor surfaces for the developer (ink) delineating the subject matter being reproduced. As an integral part of these processes, the photoconductive surface must exhibit particular electrical properties depending upon the characteristics of the electrographic process. Humidity can and often does affect these electrical properties to the extent that a photoconductive surface suitable in a particular electrographic process at one humidity may be unsuitable at a different humidity. In general, it is at high relative humidities that the quality of reproduction deeriorates, often to the point that little or no image delination is obtained.

It is entirely too expensive to control humidity by external means, particularly for electrographic processes employed for general copying. This invention relates to a composition and technique for improving humidity resistance at the source by providing an improved humidity resistant photoconductive composition.

Exemplary electrographic processes are the electrolytic electrophotographic process described in US. Pat. No. 3,010,883, the electrostatic electrophotographic processes such as is illustrated by US. Pat. No. 3,152,894, and the dynamic electrographic (electropowder) process described in US. application Ser. No. 668,183 and French Pat. No. 1,456,993. Although the photoconductive composition of this invention has general applicability to electrographic processes operating on the above principles, it is particularly adapted as an intermediate for the production or multiple copies in the electropowder process.

In this latter process, a photoconductive sheet is used as a field electrode and is exposed to a light image to create a differentially electronically conductive pattern on the field electrode. While the differentially conductive pattern is present in the photoconductive sheet or field electrode, the surface of the field electrode is uniformly contacted with a conductive applicator containing electrically conductive developer or transfer medium while an electrical field is created by applying a direct current electrical potential between the field electrode and the applicator containing the conductive developer. An electrically conductive path is created between the surface of the field electrode and the applicator. Separation of the developer applicator from the field electrode surface at the end of the development stage is made while the electrical field is maintained. The developer selectively deposits on the field electrode surface in an image-wise manner corresponding to the original light image, thus providing a visible reproduction. No electrostatic pre- 3,736,134 Patented May 29, 1973 charging of the field electrode surface is either indicated or desirable. If desired, the developer material may be retained on the field electrode surface or may be transferred to a separate receptor sheet and fixed thereon by chemical or physical means to provide the desired print.

The problem of humidity as its affects electrostatic copying is discussed in U.'S. Pat. 3,248,217, wherein a humidity resistant photoconductive sheet is disclosed, the photoconductive coating consisting essentially of a photoconductor, generally zinc oxide, an emulsifiable polyethylene binder, a water-insoluble fatty acid, and a waterinsoluble dispersant formed from a water-soluble lower alkyl silicone resin. The water-insoluble fatty acids are said to contribute to the water resistance of the final coating. Upon drying and curing of the coating the silicone resins form a water-insensitive coating around the photoconductive zinc oxide particles. It is recognized that silicones in general afford a measure of humidity protection.

In the present invention, certain additives are employed to extend humidity protection to photoconductive titanium oxide. Titanium dioxide has been found to undergo a gradual decrease in image density with increasing humidity as illustrated by the following data:

Image density Temp. F./Rel. humidity: (maxi-mum) 72 40% 1.09 O.D.U. /80% 0.76 O.D.U. v80/61% 0.

With the use of an inorganic oxide other than titanium dioxide in combination with a carboxylic acid, or salt thereof, the humidity resistance of photoconductive titanium dioxide is improved as will be shown hereinafter.

The photoconductive titanium dioxide, inorganic oxide other than titanium dioxide, and carboxylic acid or salt thereof may be combined with a binder in the form of a coating on a substrate suitable for use in an electrographic process. The characteristics of the substrate will depend on the electrographic process in which the photoconductive composition is to be employed. Belts, sheets, rollers, and drums are typical forms of substrates for photoconductive compositions. In the case of the dynamic electrographic process described in commonly assigned US. application Ser. No. 668,183, the photoconductive composition takes the form of a surface coating on a dielectric film to provide an electrographic sheet or field electrode. The electrographic sheet preferably includes an electronically conductive layer bonded to the underside of the dielectric layer, i.e., the face opposing that on which the photoconductive composition is coated.

The accompanying drawing illustrates this preferred electrographic sheet. Referring to the figure, there is shown an electrographic sheet 1 having a photoconductive image layer 3, a dielectric layer 5, and conductive layer 7 bonded to the dielectric layer 5.

The image layer formed from the photoconductive composition of this invention should upon light exposure provide a differentially conductive pattern wherein the conductive regions are at least twice as conductive as the nonconductive regions, preferably at least 10 times as conductive. The relatively conductive regions of the image layer (containing the conductive pattern) should be as conductive as possible and at least have a maximum resistivity at the surface of 10 ohm-cm., preferably 10 ohm-cm. The relatively nonconductive regions should generally have a minimum resistivity at the surface of 10 ohm-crn., although for special conditions, a resistivity of 10 or 10 ohm-cm. would be suitable. These resistivity values are measured under an electric field and for an applied time corresponding to that to be used in the electropowder process, and it is to be remembered that the conductive regions are at least twice as conductive as the nonconductive regions within the above over-all ranges, and the conductive regions are at least about 10 times as conductive as the dielectric layer. For best results, the limits of transverse resistivity at the surface of both the nonconductive regions and the conductive regions of the electrode are between about 10" and 10 ohm-cm.

For the preferred embodiment herein where the photoconductive sheet is to be employed in the electropowder process, the base for the photoconductive surface coating comprises a dielectric layer alone or in combination with a conductive layer bonded to the undersurface of the dielectric layer. The conductivity of the dielectric layer should be about 10 (ohm-cm.)- or lower, and preferably 10" or lower, a conductivity fulfilled by most good dielectric or insulating materials. It is preferred that the dielectric layer exhibit such conductivity independent of the ambient conditions, i.e., temperature and relative humidity. In any case, the conductivity of the dielectric layer should be at most about .1 the conductivity of the conductive layer when present.

A variety of materials satisfy the requirements for the dielectric layer of this invention including paper, polyesters such as those available commercially under the trade names Mylar and Scotchpar, polypropylene, polycarbonate, cellulose acetate, and polystyrene. Polyesters are preferred.

The conductive layer may be supporting or nonsupporting, for example, a thin vapor coated metal layer or a thicker conductive paper support. Generally, the conductive layer is bonded to the dielectric layer which bears the photoconductive surface layer. For some electrographic processes, the photoconductive composition may be applied directly to a conductive substrate. For the electropowder process, the conductivity of this layer should be such that no more than a small voltage drop occurs across it when the developing current passes through it. Small in this sense is relative to the voltage drop in other parts of the circuit through which current passes. Preferably, the voltage drop across the conductive layer should be no more than about 4 of the development voltage. Generally, the resistivity of the conductive layer should be less than about ohm-cm., depending upon processing conditions and thickness of the layer. Exemplary conductive materials include conductive paper, paper-metal foil laminates and foils, coatings or other forms of metals such as copper, iron, silver, and aluminum. The conductive layer may be in the form of a plurality of plies of conductive material or a single layer made from a single material or a mixture of materials.

The titanium dioxide employed in the present invention is photoconductive. Preferably, the titanium dioxide is of the type described in commonly assigned US. application Ser. No. 867,738 which will enable the production of multiple copies per exposure of the electrographic sheet in the dynamic electrographic process. This titanium dioxide is characterized as having a characteristic relaxation time of less than 9 minutes, and preferably less than 6 minutes. The determination of characteristic relaxation time is fully described in said application Ser. No. 867,738. Employing titanium dioxide exhibiting such a characteristic relaxation time, in combination with the organic acids or salts thereof, has enabled the production of several copies of the original from a single exposure of the electrographic sheet.

Included in the photoconductive composition is a carboxylic acid or salt thereof. In general, carboxylic acids which will convert to the metal salt by reaction with the corresponding metal oxide may be employed. Exemplary carboxylic acids are aliphatic, cycloaliphatic, aromatic acids such as acetic, propionic, butanoic, hexanoic, octanoic, lauric, stearic, benzoic, oleic, cerotic, caproic, linoleic, abietic, rosin acids, dehydroabietic acid, 1- nap th c, Z- Ph AQi q-nitrcbenzc c d m-nitmbeuzoic acid. The carboxylic acids having two or more atoms may be employed, preferably 2 to 30 carbon atoms, and most preferably 6 to 20 carbon atoms. Exemplary salts are ammonium salts and metal salts. Examples of the latter include alkali metal, alkaline earth metal, aluminum, gallium, and zinc salts. Preferred are the zinc salts of the above mentioned carboxylic acids, especially zinc abietate and zinc rosinate.

Also present in the photoconductive composition is a metal oxide other than photoconductive titanium dioxide, suitable metal oxides including barium oxide, calcium oxide, magnesium oxide, lead (II) oxide, lead (IV) oxide, mercuric oxide and zinc oxide.

The photoconductive titanium dioxide, carboxylic acid or salt thereof, and metal oxide as described herein may be disposed in an insulating binder, generally an insulating resin binder, to provide a coating for an electrographic sheet. Exemplary binders include chlorinated polyethylene, polyvinyl acetate, Lexan polycarbonate, polystyrene, styrene copolymers (e.g., styrene-butadiene copolymer, styrene-n-butyl acrylate copolymer, styrene-isoprene copolymer), acrylonitrile copolymers, polymethyl meth acrylate, polybutyl methacrylate, polyhexyl methacrylate, polydimethylaminoethyl methacrylate, polymethyl acrylate, polycyanoethyl acrylate copolymers, and polyvinylidenechloride polymers. Preferably, the binders have an acid number below 70, and most preferably below 40, and are free of emulsifying agents. Preferred polymeric binders are polystyrene-butadiene copolymers, chlorinated polyethylene, polyvinyl acetate and Lexan polycarbonate.

In addition to the foregoing components, the photoconductive composition may contain other additives. One preferred additive is a class of materials known as dye sensitizers. Their concentration should preferably be below 3 10* most preferably .3 1'0" grads of dye per gram of titanium dioxide.

The carboxylic acid or salt thereof levels of about 185x10 preferably 3.7 l0- equivalents per square meter of titanium dioxide surface have proved suitable. The amount of carboxylic acid or salt thereof may also be expressed in terms of an amount suflicient to provide at least one-half and preferably at least one monomolecular surface coverage of the photoconductive titanium dioxide. The inorganic metal oxide should be present to the extent of at least one-half and preferably at least one chemical equivalent of the carboxylic acid or salt thereof. The amount of inorganic metal oxide may also be expressed as at least .15 by weight based upon the combingd weight of titanium dioxide and inorganic metal oxi e.

The titanium dioxide should be present to the extent sufiicient to provide a developable image in the electrographic process. Generally, the titanium dioxide may be present to the extent of about 20 to about volume percent of the combined volume of titanium dioxide and insulating resin binder, preferably 40 to 60 percent, and most preferably 50-55%.

. The following examples are provided to illustrate the invention.

EXAMPLES 1-14 A smooth dispersion is prepared by ball milling for 16 hours 38 grams titanium dioxide, 12.6 grams chlorinated polyethylene binder (available under the trade name Tyrin QX 2243.25), ml. toluene, .025 gram of Rhodamine B dissolved in 5 ml. methylene chloride, and 2.85 10- chemical equivalents of the zinc salt of the carboxylic acid (3.7 10- equivalents per meter of titanium oxide), and 2.85 1() chemical equivalents of zinc oxide, as shown in Table 1.

Photoconductive copy sheets of each of these compositions are prepared by applying a uniform coating (about .7 mil thick dry) of the dispersion to a 1 mil thick film of polyethylene terephthalate (resistivity of 10 ohms/ square) having a thin vapor deposited aluminum coating (surface resistivity 5 ohms/ square) on the underside and drying at room temperature. These steps are conducted under safelight conditions.

The sheets are then processed according to the elec- Rhodamine B dye (0.5% by volume in methylene chloride), carboxylic acid or salt thereof and zinc oxide in the amounts shown in Table 3. The sheets are processed according to the foregoing examples at the temperatures and humidities shown in Table 3, and the image density tropowder process described in US. application Ser. No. 5 values obtained. 668,183. Process conditions are: 1500 volts, development voltage, 30 mil development gap, 15 mil doctor blade TABLE 3 gap, temperature and humidity as shown in Table 1. The L Dmax. developer powder is a thermoplastic, electrically conduc- 10 Eq o tive, magnetically attractable powder ranging from 2-12 Example Addltwes Isms F'/51% 80 F'/80% microns in diameter available under the trade name Type 22 Abietic x 1 Q99 083 842 Imaging Powder. The electrographic sheets are ex- 23 Abietic acid ,333} Q97 000 posed to a tungsten iodide light for the optimum ex- 24 Zincmsmate {g- X -a L02 L03 posures for each sheet. The image densities (I.D.) of the 25 zinc msinate 23388} 1,02 092 test sheets are measured in the standard manner with a Macbeth Reflection Densitometer (Model RD-100) with the results shown in Table 1. From the data of the foregoing examples, it can be seen TABLE 1 that the combination of the carboxylic acid or salt thereof I'll max. and the metal oxide provides an image density greater than 70 F/ 80 Fl 80 I 81 I ghfetfigrrestptfndmdg image density OEtalIigtElt 1n tlcllet absence M me a on e a one or more umi 1 an em era- Example Addltwes 50% 62% 71% 81% ture levels. The level at which the impro vement is seen gm aceette/Zn0 8-3; 8-32 g 8 varies with the composition, as can be observed from a: Z3 l ih ti r telirit ji: 1: 02 0188 ,4 the data. The environmental conditions employed in the g" gm gutyr t n ggg 8- 0 8 8 tests are those which are encountered at various times 6 2 323832 0 0 0 of the year in nearly all countries. It is apparent that a 7-- Zn va at /Z 10- 99 7 0 g drop in image density of the order shown constitutes a g: 3253353 81g; 056 Q01 0 slelrioilis if not insurmountable barrier to general use of 10- Zn laurat 0. 0 0 0 t e e ectrographic recess. The im rovement in humidit stearate/Zno"" 813% 512. 3 3 resistance as reflec ed in image deiisity of the photocon 2 1%? 3. 3 d'uctive compositions of this invention appears to be observable at all levels of concentration of metal oxide and carboxylic acid or salt at one or more humidity levels. As EXAMPLES 15-21 the humidity is increased to the higher levels, the mag- Dispersions are prepared as in the foregoing examples nitude of the improvement increases. containing 38 grams titanium dioxide (characteristic re- Considerations other than humidity resistance may diclaxation time of 1.25 minutes), 12.6 grams of the binder tate limiting the quantity of carboxylic acid or salt and of Example 1, 180 m1. toluene, .025 gram of Rhodamine metal oxide. One factor in particular is the effect of such B in 5 ml. methylene chloride, 2.85 10-3 equivalents 40 additives on light sensitivity. It has been observed that (0.86 gram) abietic acid, and 5.7 10" equivalents of light sensitivity does decrease as the amounts of additives the metal oxide shown in Table 2. increases. Thus, for purposes of this invention, it is pref- Photoconductive sheets of the same construction as erable that the quantities of additives be kept at or near described in Examples 1-14 are prepared with these disthe level where humidity resistance is satisfactory for the persions, and the resulting photoconductive sheets exuse at hand rather than increasing loading of the photoposed and developed as in Examples 1-14 at the temconductive composition beyond the satisfactory level to peratures and humidities shown in Table 2. By comparithe detriment of other properties such as light sensitivity. son to the control (Example 21), the photoconductive To illustrate this point, the following examples are prosheets of this invention demonstrated an improvement in vided. humidity resistance of the magnitude shown. EXAMPLES 26 33 TABLE 2 I D max I D max Photoconductive compositions are prepared by the pro- Example Oxide (71 Iii/60%} (80'F../85%) cedure of Examples 1-14 from the following ingredients 0.94 088 plus the amount of zinc oxide and TiO 1 in Table 4: ii. 812% Polyethylene binder 2 g 12.6 8-83 Toluene ml 180 1.00 0:84 Rhodamine B (0.5 in Ch Cl ml 5 Abietic acid g 0.86

1 EXAMPLES 22. 25 traihgitlcxirclgnlvdltcgiiastgamum dioxide available under the Electrographic sheets are prepared in accordance with zTmde name Tyrin (QX 2243-25)- the foregoing examples from 38 g. photoconductive tita- Photoconductive sheets are prepared and tested as in nium dioxide (trade name MSS40-5F), 12.6 g. of chlo- Examples 1-14, the optimum exposure and image density rinated polyethylene binder, 180 ml. toluene, 5 ml. at various conditions being shown in Table 4.

TABLE 4 LD. max. Wt. Wt. Percent Exposure Example T102 2110 ZnO (f.c.s.) F./66% 80 F.l72% 80 F./%

0 17.5 0. 4s 0 0 a 17.5 0.89 0 0 1 30 0.97 0.01 0 5 40 0.99 0. 98 0.92 10 50 1. 01 1. 0o 0. 92 20 00 0.99 0. 93 0. 94 5o 60 1. 06 1. 09 1. 05 75 40 1.13 1. 1e 1. 14

7 EXAMPLES 34-38 The following materials are introduced in the order listed into a gal. container fitted with an air stirrer:

8 What is claimed is: 1. A photoconductive composition comprising photoconductive titanium dioxide disposed in an insulating binder, said titanium dioxide being present to the extent Na Quantity 5 of about 20 to about 80 volume percent of the combined Toluene --g-- 6617 volume of titanium dioxide and binder, a first additive Y P Q 7 trade m 521 of a carboxylic acid or metal salt thereof present to the Zinc foslllate Camp, UlllVfiZ extent of at least about 1.85 X equivalents per square trad nartl meter of titanium dioxide surface area, and a second 2 (Natlonal Lead, trade 10 additive of an inorganic metal oxide other than titanium name) g-- 1562 dioxide present to the extent of at least about one-half Rhodamine B -g-- of the equivalents thereof of said carboxylic acid or metal Methanol 9 salt thereof and less than 20% by weight based on the ZIIO trade As Shown 1n combined weight of titanium dioxide and inorganic metal table 5 15 oxide.

After premixing the Slurry is homogenized by 2 passes The composition of claim 1 wherein said carboxylic through the homogenizer (Hate name Manton Gau1in acid or metal salt thereof 1s present to the extent of at S15) at 3000 p.s.i. The dispersions thus prepared are alf' aboui equlYalents P Square {meter of lowed to cool to room temperature before coating titanium dioxide and said inorganic metal oxide other The dispersions are then coated at a wet thickness than titanium oxide is present to the extent of about oneof 3 mils on the polyester Side of aluminum vapor coated half the chemlcal equivalents of said carboxyllc acid or 1 mil polyester film (dry coating thickness approxiately Salt thereof- 07 mil) Drying times of approximately .1 hour are 3. The composition of claim 1 wherein said carboxylic quired at ambient eonditions acid or metal salt thereof is present in an amount suf- The eleetrographie Sheets are imaged and developed in ficient to provide at least a monomolecular layer thereof the electropowder process at the humidities and temperaon 531d tltamum Q tures shown in Table 5. The conditions for the electro- The composltlon of clam 1 Whemm Said carboxyhc Powder test machine acid or metal salt thereof has from 2 to about carbon atoms.

gevflopment voltage 38 9 Volts 3O 5. The composition of claim 1 wherein said first addieve opment gap i tive is a zinc salt of a carboxylic acid and said second Doctor blade gap 0.015 m. e

1 d 16 5 addrtlve is zinc oxide. Deve opment spee 6. The composition of claim 1 wherein said first addi- After development, the developer powder (same as tive is a carboxylic acid or zinc salt thereof having from in Examples 1-14) is fused to the electrographic sheet 6 to 20 carbon atoms, and said inorganic metal oxide is and the image density determined using a Macbeth RD- zmc oxide. 100 densitomer. 7. The composition of claim 1 wherein said inorganic TABLE 5 ID. max. Percent Exposure ZnO (i.e.s.) 80 I-./54% 80 F.l61% 80 F./6S% 80 F./75% 80 F./80%

0 16 0.83 0.24 0 0 0 0. 15 16 0. 97 0. 83 0. 34 0. 02 0 0. 30 1s 1. 02 0. 98 0. 86 0. s5 0. 34 0. 60 20 1. 04 1. 04 1. 03 1. 03 1. 02 a. 0 40 1.08 1. 04 1. 05 1.06 1. 03

By weight based on the combined weight of titanium dioxide and 'zinc oxide.

EXAMPLES 39-43 Electrographic sheets are prepared and tested as in Examples 1-14 using the following ingredients:

TiO, (trade name 540-5K) -Jg-.. 36:1 8. The composition of claim 1 wherein said first addi- ZnO (USP-12) g 1.9 tive is an organic carboxylic acid or ammonium or metal Polyethylene binder (trade name Tyrin saltthereof having 6 to 20 carbon atoms and said second OX--2243.25) g 12.6 additive is at least one inorganic metal oxide selected from Toluene ml 180 the class consisting of barium oxide, calcium oxide, mag- Rh'odamine B (0.5% by vol. in OH CI .ml 5 nesium oxide, lead (II) oxide, lead (IV) oxide, mer- Zn rosinate As shown in curic oxide, and zinc oxide.

Table 6 9. A photoconductive composition comprising an in- TABLE 6 Zn rosinate (equiv.lm. I.D. max.

T10: Exposure surface) (i.e.s.) 72 F./42% so" F./57% 80 F./64% 80 F./76% 80 F./83% 80 F./90%

0 20 0. 94 o 0 0 0 0 0. 92 10 20 1. 0s 0. 42 0.02 0 0 0 1. ssxio- 20 1. 07 1. 01 o. 91 0. 01 o 0 3. 7 10 25 1. 10 1.07 1. 09 1. 04 0. 9a 0. 66 7. 4 10- 40 1. 14 1. 16 1.10 1. 09 1. 09 1. 06

In addition to improvements in humidity resistance, it has also been observed that electrographic elements bearing a surface coating of the formulations of this invention are capable of improving both reusability of the elements and imaging life, i.e., the ability to achieve multiple copies per exposure of the electrographic element.

sulating resin binder having distributed therein photoconductive titanium dioxide, said titanium dioxide being present to theextent of about 20 to about by volume based on the combined volume of said titanium dioxide and insulating resin binder, a first additive of a carboxylic acid or metal salt the eof presen to the extent of at least about 1.85 X equivalents per square meter of titanium dioxide surface area, and a second additive of an inorganic metal oxide other than titanium dioxide present to the extent of at least about one-half of the equivalents thereof of said carboxylic acid or metal salt thereof and less than 20% by weight based on the combined weight of titanium dioxide and inorganic metal oxide.

10. The composition of claim 9 wherein said carboxylic acid or metal salt thereof is present in an amount sufficient to provide at least a monomolecular layer thereof on said titanium dioxide.

11. The composition of claim 10 wherein said first additive is a zinc salt of a carboxylic acid and said second additive is zinc oxide.

12. The composition of claim 10 wherein said first additive is a carboxylic acid or zinc salt thereof having from 6 to 20 carbon atoms, and said inorganic metal oxide is zinc oxide.

13. An electrographic sheet having a surface layer comprising an insulating resin binder having distributed therein photoconductive titanium dioxide, said titanium dioxide being present to the extent of about 20 to about 80% by volume based on the combined volume of said titanium dioxide and insulating resin binder, a first additive of a carboxylic acid or metal salt thereof present to the extent of at least about 1.85 x 10" equivalents per square meter of titanium dioxide surface area, and a second additive of an inorganic metal oxide other than titanium dioxide, said surface layer being bonded to a dielectric layer present to the extent of at least about one-half of the equivalents thereof of said carboxylic acid or metal salt thereof and less than 20% by Weight based on the combined Weight of titanium dioxide and inorganic metal oxide.

14. The sheet of claim 13 wherein said inorganic metal oxide is at least one member selected from the class consisting of barium oxide, calcium oxide, magnesium oxide, lead (II) oxide, lead (IV) oxide, mercuric oxide, and zinc oxide.

15. An electrographic sheet having a surface layer comprising an insulating resin binder having distributed there in photoconductive titanium dioxide, said titanium dioxide being present to the extent of about 20 to about 80% by volume based on the combined volume of said titanium dioxide and insulating resin binder, a first additive of a carboxylic acid or metal salt thereof present to the extent of at least about 185x10 equivalents per square meter of titanium dioxide surface area, and a second additive of an inorganic metal oxide other than titanium dioxide present to the extent of at least about one-half of the equivalents thereof of said carboxylic acid or metal salt thereof and less than 20% by weight based on the combined weight of titanium dioxide and inorganic metal oxide, said surface layer being bonded to a dielectric layer and a conductive layer bonded to the underside of said dielectric layer.

16. A photoconductive composition comprising photoconductive titanium dioxide disposed in an insulating binder, said titanium dioxide being itself present to the extent sufficient to provide a developable image in an electrographic process, a first additive of a carboxylic acid or metal salt thereof present to the extent of at least about 1.85 10 equivatents per square meter of titanium dioxide surface areas, and a second additive of an inorganic metal oxide other than titanium dioxide present to the extent of at least about one-half of the equivalents thereof of said carboxylic acid or metal salt thereof and less than 20% by weight based on the combined weight of titanium dioxide and inorganic metal oxide.

17. An electrographic sheet having a surface layer comprising photoconductive titanium dioxide disposed in an insulating resin binder, said titanium dioxide being itself present to the extent sufficient to provide a developable image in an electrographic process, said titanium dioxide being present to the extent of about 20 to about by volume based on the combined volume of said titanium dioxide and [insulating resin binder, a first additive of a carboxylic acid or metal salt thereof present to the extent of at least about 1.85 10- equivalents per square meter of titanium dioxide surface area, and a second additive of an inorganic metal oxide other than titanium dioxide present to the extent of at least about one-half of the equivalents thereof of said carboxylic acid or metal salt thereof and less than 20% by weight based on the combined Weight of titanium dioxide and inorganic metal oxide, said surface layer being bonded to a dielectric layer.

References Cited UNITED STATES PATENTS 3,198,632 8/1965 Kimble et al. 96-1 3,079,253 2/ 1963 Greig 96-1 3,220,830 11/ 1965 K-ashiwabana 96-1.8 3,245,784 4/1966 Stricklin 96-1.8 3,248,217 4/1966 Shulman 96-1.8 2,901,348 8/1959 Dessauer et al. 96-15 3,241,458 3/ 1966 Borharth et al. 96-18 3,174,856 3/1965 Horne et al. 961.8 3,234,017 2/196-6 Heyl et a1 252-501 X 3,378,371 4/1968 Jarvis 96-1.8 3,418,147 12/1968 Fields 106-300 X 3,492,264 1/ 1970 Hahn 1-06-309 X 3,561,968 2/ 1971 Dantro 252-501 X 3,632,527 1/1972 Alpert et a1 252-501 3,607,262 9/1971 Veda 96-1.8 3,569,803 3/1971 Sato et al 96-18 X 3,653,895 4/ 1972 Brandon 961.8

OTHER REFERENCES Klein, Otto 0.: Effect of Moisture and Type of Binder on Electrophotographic Behavior, TAPPI, vol. 47, No. 9, September 1964, pp. -148.

CHARLES E. VAN HORN, Primary Examiner US. Cl. X.R. 96-15; 252-501 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,7l3 fl-3 I Dated May 29, 1973 Invenwfls) Donald W. Gosselink and Einar D. Home It is certified that error appears in the aboVe-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 51, "or" should read of Col. 2, lines'2.8,29, in the table,

80/80% 0.76 0.D.U 8Q/6l.% O. 6 O.D.U 80/6l% o shwld read 80/80% 0 7 Signed and sealed this 21st day of May 1972+.

1 SEAL! Attesat:

L'JDU'IARD H.FLETC.T.li3R,-Hi. C. MAHSHAIL DANE Attestlngg Officer Commissioner of Patents USCOMM-DC BOJ 6-P69 

